478 



Fishery Bulletin 93(3), 1995 



B 



24.9 



23 9 



-83.5 -830 -82 5 -82 -81-5 -81.0 



-83 5 -83 -82 5 -82 -815 -810 



Solenocera sp. 



-83 5 -83 -82 5 -82 -815 -81.0 



-83.5 -83.0 -82.5 -82.0 -81.5 -81.0 



Longitude 

 Figure 4 



Horizontal distribution and relative abundance (larvae/10 m 2 ) of 

 zoeal and mysid stages of (A) the rock shrimp Sicyonia sp. and 

 (B) the humpback shrimp Solenocera sp. for the four legs of the 

 LH3 cruise, 29 May-30 June 1991. The symbols are proportional 

 in size to the abundance range and are positioned at the sam- 

 pling stations. The stars = no catch. 



Tortugas and NW Patch transects and at the 

 two stations sampled on the track of the drifter 

 Halley showed the same modal progression of 

 zoeae to postlarvae within 15 days. This period 

 corresponds to the time reported by Ewald 

 (1965) for zoeae III to become postlarvae I at 

 26°C. This time period for larval development 

 from zoeae to postlarvae also agrees remark- 

 ably well with the trajectory time of the drifter 

 recirculating in the interior of the gyre. The tim- 

 ing of the modal progression of larval stages 

 occurring within those 15 days of gyre recircu- 

 lation at the spawning area, as shown by the 

 drifter, may indicate that P. duorarum larvae 

 were recirculating in the interior of the gyre 

 during development. Interestingly, after the 

 drifter broke out of the gyre circulation it moved 

 toward the east and north toward the Florida Bay 

 shrimp nursery grounds, suggesting a local re- 

 cruitment pathway for this species. 



Retention of P. duorarum larvae at the 

 spawning area by the Tortugas Gyre for some 

 days after hatching may enhance the survival 

 of these larvae because food resources are avail- 

 able in the uplifted nutracline where Lee et al. 

 (1994) found maximum concentrations of chlo- 

 rophyll and copepod nauplii. Furthermore, 

 postlarvae located in the northern (nearshore) 

 portion of the gyre may increase their chance 

 of settling either by escaping the offshore flow 

 on the western side of the gyre entirely or by 

 resisting the offshore flow, thereby drifting to 

 the west rather than being swept offshore 

 (Porch, 1993). Thus, the primary pathway for 

 P. duorarum larvae to reach the nursery areas 

 of Florida Bay may include retention at the 

 spawning area by recirculation in the Tortugas 

 Gyre followed by movement onto the Southwest 

 Florida shelf and Florida Bay by wind and tidal 

 currents. Those larvae that are advected east- 

 ward by the Florida Current may reach the 

 upper and middle Keys. The latter alternative 

 could explain the great number of postlarvae 

 found in the middle Keys by Munro et al. ( 1968) 

 and Roessler and Rehrer (1971). 



Sicyonia sp. larvae showed a coastal and shal- 

 low distribution. Young zoeae were generally 

 restricted to the inshore stations, indicating 

 that this species may spawn near the Dry 

 Tortugas Grounds. Myses showed the highest 

 concentrations inshore, with a maximum con- 

 centration at the Marquesas transect. Larval 

 stages at the two stations of the drifter showed 

 a similar trend to that off! duorarum. The time 

 of development of S. brevirostris from spawn- 



